For recording properties of defined points in a measurement environment, particularly of data with a spatial reference, a multiplicity of measurement methods have been known since ancient times. In this case, the position and orientation of a surveying instrument and also direction, distance and angle in relation to measurement points are recorded as spatial standard data. One generally known example of such surveying instruments or geodetic instruments is the theodolite or a total station. Such instruments have angle and distance measurement functions that allow determination of direction and distance in relation to a selected target. In this case, the angle and distance variables are ascertained in the internal reference system of the instrument and, for absolute position finding, also need to be combined with an external reference system, for which purpose the position of the surveying instrument in the external reference system normally serves as a basis.
In principle, the station coordinates of the measuring instrument can be computed as what is known as free deployment from measurements pertaining to points that are already referenced absolutely in the deployment environment. These may be fixed and distinguished points that exist in the terrain, for example church spires or objects installed specifically for geodetic measurements, e.g. target markings on a building site. For correct position finding, the measurement data each need to be explicitly associated with the relevant reference points in this case. Such referencing for every single point measurement usually requires at least partial manual implementation, which is time consuming and error prone.
Therefore, EP 2142884.B1 discloses a position finding method that takes away from the necessary combination of point identification and recording of the measurement data that needs to be observed for the measurement. To this end, the necessary association of the measured points with their corresponding elements in one set of reference points is effected, following or progressively during deployment measurement, using the relative position of the points in relation to one another. The procedure can be performed in an automated fashion by a surveying instrument with an automatic target recognition function. A disadvantage of this method is that there needs to be a plurality of absolutely referenced points in the surroundings, and these points must furthermore be measurable. Furthermore, for automation, they need to be provided with markings that the surveying instrument can target, e.g. retro reflective prisms. Another disadvantage is that position finding accordingly requires a plurality of geodetic measurements to be performed, which normally requires expert knowledge and increased time involvement. In addition, performance of the position finding method disclosed in EP 2142884.B1 requires the appropriate set of reference points to have been selected in advance, that is to say in this respect requires certain prior knowledge of the location.
The position of a surveying instrument can alternatively be determined by means of a GNSS receiver mounted on the surveying instrument using individual satellites as reference points. However, a disadvantage is the lower resolution, particularly in respect of height determination, in comparison with referencing by means of geodetic measurement. In addition, the process is tied to the reception of GNSS signals, which is not available everywhere.